191 
>5 J4 
py 1 



THE EFFECT OF CERTAIN COLLOIDAL 

SUBSTANCES ON THE GROWTH 

OF WHEAT SEEDLINGS 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 
OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



BY 

DAVID STOUT JENNINGS 



OCTOBER, 1917 



Reprinted from SOIL SCIENCE. Vol. VII, No. 3. March, 1919 



THE EFFECT OF CERTAIN COLLOIDAL 

SUBSTANCES ON THE GROWTH 

OF WHEAT SEEDLINGS 



A THESIS 

l 
PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 

OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



BY 

DAVID STOUT JENNINGS 



OCTOBER, 1917 



Reprinted from SOIL SCIENCE. Vol. VII, No. 3. March, 1919 



ll 






P? of -•. 

APS 6 1920 



Reprinted from Soil Science, 
Vol. VII, No. 3, March, 1919 



THE EFFECT OF CERTAIN COLLOIDAL SUBSTANCES ON THE 
GROWTH OF WHEAT SEEDLINGS 1 

DAVID STOUT JENNINGS 

Utah Agricultural Experiment Station 

Received tof publication March 5, 1919 

The power of a soil to retain water against the force of gravity, to counteract 
the bad odors of decaying organic matter, and to modify the concentration of 
a solution with which it is in contact, is due wholly or in part to the phe- 
nomenon of absorption. Since the chemical composition of the soil is so 
complex it is difficult to ascertain to what extent the process of absorption 
from solution by the soil in a given case is chemical and to what extent it is 
physical. The absorption by some of the relatively insoluble soil con- 
stituents such as silica, and iron and aluminum oxides is probably physical 
and is termed adsorption. Within the last few years considerable work has 
been done pertaining to the absorption of salts and ions from solution by 
soils and other finely divided materials. Little attention, however, has been 
given to the effect this might have upon plant growth. 

As a rule, adsorption is positive, that is, the concentration of a salt in the 
bulk of a solution is usually reduced by introducing absorbing surfaces into 
the solution. Consequently, the concentration of the salt at the interface 
is greater than that of the bulk. The object of this work was to attempt to 
answer the following question: Is the change in concentration due to solid 
adsorbing surfaces sufficient to modify the production of dry matter in a 
plant? 

REVIEW OF LITERATURE 

Gregoire (5) grew barley to maturity in Detimer's nutrient solution to 
which was added three-tenths of a per cent of silica in one treatment, and 
the same per cent of aluminum oxide in another treatment. Solution cul- 
tures were used as checks. There was a decided increase in the yield of dry 
matter in the silica cultures, and an increase in the case of the aluminum 
oxide cultures, but less than for the silica. More than 43.5 per cent of the 
ash of the plants from the silica culture consisted of silica, while less than 5 
per cent of silica was present in the ash of the check. This author believes 
that the increase was due largely to the absorption of silica by the plants 
and its consequent utilization in growth. The ash of the plant in the alumi- 

1 A thesis submitted to the faculty of the Graduate School of Cornell University in partial 
fulfillment of the requirements for the degree of Doctor of Philosophy. 

201 



202 DAVID STOUT JENNINGS 

num oxide culture contained 6 per cent alumina, while there was less than 1 
per cent alumina in the ash from the check. 

By growing wheat plants in solutions of several different densities, Lyon 
and Bizzell (8) showed that for the nutrient solution used the dry matter 
produced per unit of transpiration increased with the density. An increase 
in this ratio is considered indicative of greater density of the nutrient solution. 
They found that plants grown in crushed quartz had a lower transpiration 
ratio than when grown in nutrient solution of the same concentration. It 
appeared, therefore, that the actual densities in the region of the absorbing 
surface of the roots may be greater in the case of quartz. Plants grown in 
crushed quartz develop an abundance of root hairs and the root hairs come in 
intimate contact with quartz grains. It is possible, therefore, that the root 
hairs are in the absorbed layer, and are, therefore, feeding from a denser 
solution. 

McCall (9) grew wheat plants in Shive's 3-salt solution when a solid medium 
representing somewhat the condition of the soil, but without the biological 
complications was present. He used a granite-ware pot provided with a 
pipe at the bottom for drainage. The solution was renewed every third day. 
The dry weights of the plants grown in the quartz sand were compared with 
those obtained by Shive. Sand cultures gave a greater dry weight. It is 
suggested by the author that the thickness of the adsorbed layer is less than 
the outer cell wall covering the adsorbing protoplasm, and since the absorbing 
protoplasm does not come in direct contact with this concentrated layer, the 
salts here are unavailable except in so far as the slow process of diffusion takes 
place. 

It is also suggested in this article that selective adsorption may be an im- 
portant factor in modifying plant growth. Thus the author calls attention 
to the fact that a better growth was produced in the sand than in the water 
cultures as the ratio of calcium nitrate to magnesium sulfate increased. This 
is explained by assuming that the N0 3 radicle produces a beneficial effect, 
that the magnesium sulfate antagonizes this effect, and that the magnesium 
sulfate more than the N0 3 would be adsorbed by the sand, and, therefore, 
less magnesium sulfate would be present in a condition to antagonize the 
favorable influence of the nitrate radicle. The results giving rise to this 
suggestion are subject to criticism since there is no record of the treatment 
having been duplicated. 

Gile and Carrero (3) grew rice plants in acid, neutral and alkaline nutrient 
solutions when supplied with 0.002 gm. and 0.008 gm. of iron per liter from 
the following sources of iron: ferrous sulfate, ferric chloride, dialyzed iron, 
ferric citrate, ferric tartrate. The dialyzed iron was prepared by the ordinary 
method. It was entirely inadequate for the plants, for they were strongly 
chlorotic at all times. 

Negeli (10), Dandeno (2), True and Oglevee (12, 13), Breazeale (1), 
Livingston (7), Jensen (6), and others have shown that the introduction of 



EFFECT OF COLLOIDAL SUBSTANCES ON WHEAT 203 

finely divided substances like carbon black into nutrient solutions causes 
increased growth. This effect has been attributed to the action of the solid 
on certain organic and inorganic toxins. 

True and Oglevee (13) advanced the theory that the adsorbing substances 
increase the growth rate by reducing the concentration of the toxic material, 
acting in the same way as the addition of water would by leaving a fewer 
number of ions or molecules in the free solution. 

According to this theory it would be possible to introduce a solid substance 
into a nutrient solution and reduce the actual concentration of the solution in 
the region of the absorbing surface. If the theory is correct, this application 
is true, it being only necessary to select the proper adsorbent. 

Dandeno (2) suggests that the increase in growth may be due to a decrease 
in the diffusion rate, while Jensen (6) adds a third possibility: viz., chemical 
change induced by the presence of the finely divided material. 

The literature fails to give conclusive evidence as to whether the intro- 
duction of a solid adsorbent into a nutrient solution increases or decreases 
the density of that solution at the absorbing surface of the roots. The 
present work was intended as a contribution to this subject. 

PLAN OF THE INVESTIGATION 

Baker's analyzed salts were used in making up the nutrient solution. The 
salts were weighed and dissolved in distilled water, giving a stock solution 
for each salt. The following table shows the concentration and composition 
of each stock solution: 

Calcium nitrate 216 gm. in 2000 cc. of water 

Potassium chloride 60 gm. in 2000 cc. of water 

Magnesium sulfate 48 gm. in 2000 cc. of water 

Ferric sulfate 4 gm. in 1000 cc. of water 

Mono potassium phosphate. .« 60 gm. in 1000 cc. of water 

A complete nutrient solution containing about 4500 parts per million was 
made up by adding 25 cc. of each solution to distilled water, as follows: The 
calcium nitrate and potassium chloride solutions were added to 250 cc. of 
distilled water. The ferric sulfate, magnesium sulfate and potassium phos- 
phate solutions were diluted each with 175 cc. of distilled water and put in 3 
different containers. The diluted ferric sulfate and magnesium sulfate solu- 
tions were mixed and then added to the potassium chloride and calcium 
nitrate mixture. Finally, the potassium phosphate solution was added and 
the mixture shaken. At the latter addition there was always a slight pre- 
cipitation. The solution was not filtered but was always shaken thoroughly 
before using. 

Galgalos wheat was used. The method of germinating and growing the 
wheat up to the point of placing it under treatment was the same in all cases 
and was as follows: A few hundred clean seeds were placed in a wide-mouth 
bottle provided with a cork with one hole through which a piece of glass 



204 DAVID STOUT JENNINGS 

tubing was inserted, one end reaching to the bottom of the bottle. The 
other end was connected with the water tap. By providing a cork too large 
or slightly too small, the water would run over the top without allowing the 
seeds to pass out. The seeds were always kept in running water for 48 hours. 
They were then transferred to a large floating disc and here kept in running 
water until four or five centimeters in height. This required about four 
days. The floating disc was a piece of stiff wire netting covered with paraffin. 
Many small holes were made in the paraffin to furnish a contact between the 
seedlings and water. Many more plants were grown to this stage than were 
required for the experiment, which made more easy a selection of plants of 
uniform top and root growth. Strong healthy plants were always selected 
for the cultures. The endosperms were carefully removed and 6 plants 
threaded into holes in a cork that would fit the container to be used. The 
threading was most easily done by carefully pressing the tops together and 
passing them into the hole, and then working the seedling into the desired 
position. Each cork with the 6 plants was then placed in the container filled 
with tap water. It appeared early in the work that the placing of the plants 
under treatment as soon as the endosperm was removed was not satisfactory, 
for many of the plants died under these conditions, while if kept in tap water 
for a short time they developed very well. Four small sticks placed in holes 
bored near the circumference of the cork and tied together by twine furnished 
support for the tops of the growing plant. 

Wherever possible the distilled water which was to be used in culture work 
was treated either with carbon black or with precipitated oxide of iron or 
aluminum. This treatment of the distilled water consisted in adding 15 gm. 
of the material to a liter of water, shaking and allowing to stand for a few 
hours and filtering. 

The hydroxides of iron and aluminum were prepared from the chlorides of 
these elements, by precipitation from solution by NH 4 OH and then washing 
free of ammonium chloride. The iron hydroxide was used at the rate of 10 
gm. of dry material calculated as Fe 2 03 and the aluminum hydroxide at the 
rate of 8 gm. AI2O3 per liter of distilled water. They were kept moist and . 
used in the same way as the carbon black. In the following discussion the 
term "treated" nutrient solution has reference to the distilled water used. 

During the period that plants were growing under treatment, they were 
kept in the greenhouse at a temperature of about 55°F. during the night 
and 60°F. during the day. 

At harvest the tops were removed and dried at a temperature of 90°C. 
In order to obviate lack of uniformity resulting from an unequal distribution 
of heat in the greenhouse, the relative positions of the cultures were changed 
at each weighing. The cultures were weighed or the solutions were renewed 
twice each week. 

The following materials, all of which have been found by different investi- 
gators to adsorb from solution, were used in the present work: agar, silica, 
crushed quartz, and hydroxides of iron and aluminum. 



EFFECT OF COLLOIDAL SUBSTANCES ON WHEAT 



205 



Agar cultures 

The agar solution was prepared by adding to the dry agar sufficient dis- 
tilled water to make a 2 per cent solution and boiling the mixture in a double 
boiler for 2 hours. The resulting solution was then cooled to a temperature 
of 60°-75°C., and the proper amount of standard nutrient solution and dis- 
tilled water added to give the desired dilution of nutrient salts. In the 
earlier part of the work a one per cent solution of agar was used, but difficulty 
was experienced in getting the tender roots of the wheat plants to penetrate 
this medium. It was found more satisfactory to use one-half per cent agar 
as the plant roots would easily penetrate this medium. After the agar medium 
had cooled to laboratory temperature the plants which had previously been 
selected and threaded into the corks were placed in the agar. Water cultures 
of the same concentration of nutrient salts were prepared as checks, the 
plants being placed in the water and agar cultures at approximately the same 
time. In certain of the cultures the solutions were not renewed but each 
culture was weighed twice each week and water added equivalent to the loss 
in weight. 

In other cases the solutions were renewed by lifting the cork carrying the 
seedlings, discarding the old medium, rinsing the container, and adding 300 
cc. fresh medium from stock solutions of the proper strength. The results of 
these experiments are given in tables 1, 2 and 3. 

The results with agar were not entirely satisfactory, but the figures present 
some interesting indications. Referring to table 1, it will be seen that in 
concentrations of 500 p.p.m. of nutrient salts, agar was beneficial, while with 
a concentration of 2000 p.p.m. the agar was harmful. A similar effect may 
be noticed in table 2, where in the 500 p.p.m. solution, agar was beneficial 
while in the 1000 p.p.m. solution, agar was harmful. With the exception of 
the 85 p.p.m. concentration, more dilute solutions were benefited by agar, 
while the higher concentrations were injured. It is conceivable that with 
the more concentrated solutions the agar rendered the effective concentration 
at the surface of the particles so great as to become toxic to plants. 



TABLE 1 

Dry weights of wheat plants grown in solution and in agar cultures. Solution not renewed; vol- 
ume of solution 930 cc. ; each result the average of 4 cultures 



TREATMENT 



Nutrient solution + 1 per 
cent of agar 

Nutrient solution 

Nutrient solution + 1 per 
cent of agar 

Nutrient solution 



CONCEN- 
TRATION 



p.p.m. 

500 
500 

2000 
2000 



days 

30 
30 

37 
37 



DRY WEIGHT 



Tops 



0.3240 

0.1799 

0.3011 

0.3568 



Roots 



0.1262 
0.0963 

0.1133 
0.1674 



Whole 
plant 



0.4502 
0.2762 

0.4144 

0.5242 



DIFFERENCE 



+0.1740 



-0.1098 



per cent 

62.9 
-24.0 



TABLE 2 

Dry weights of wheat plants grown in a nutrient solution and in a nutrient solution with 1 per 

cent of agar. Volume of solution 500 cc.; solution not renewed; each result the 

average of 4 cultures 





CONCEN- 
TRATION 


PERIOD 
OF 

GROWTH 


WEIGHT OF 






TREATMENT 


Tops 


Roots 


Whole 
plant 




Distilled water 


p,p.m. 

85 

85 

250 

250 

500 

500 

1000 

1000 


days 

18 
18 
20 
20 
29 
29 
36 
36 
36 
36 


gm. 

0.0918 
0.1239 
0.1643 
0.1494 
0.2367 
0.2790 
0.2721 
0.3217 
0.4420 
0.3075 


gm. 

0.0311 
0.0524 
0.0488 
0.0478 
0.0604 
0.0667 
0.0569 
0.0681 
0.1076 
0.0636 


gm. 

0.1229 
0.1763 
0.2252 
0.1972 
0.2971 
0.3457 
0.3290 
0.3898 
0.5496 
0.3711 


gm. 

+0.0534 
-0.0280 
+0.0486 
+0.0608 
-0.1786 


per cent 


Distilled water + agar 


+42.6 


Nutrient solution + agar . . . 


-12.4 


Nutrient solution + agar . . . 


+ 16.3 


Nutrient solution + agar. . . 


+ 18.1 


Nutrient solution + agar . . . 


-32.4 



+ Indicates increase in agar culture compared with check. 
— Indicates decrease in agar culture compared with check. 

TABLE 3 

Dry weights of wheat plants when grown for 5 weeks in a nutrient solution and in a nutrient 

solution to which was added 0.5 per cent agar. Solution renewed twice per week; 

volume of solution 300 cc; concentration 750 p. p.m. 





LAB. NO. 


WEIGHT OF 




Tops 


Roots 


Whole plant 


Nutrient solution \ 


80 
81 
82 
83 
84 
85 
86 
87 
88 
89 


gm. 

0.4042 
0.5175 
0.4355 
0.6204 
0.5456 
0.5479 
0.4456 
0.5531 
0.5372 
0.4485 


gm. 
0.0905 
0.1133 
0.0858 
0.1401 
0.1198 
0.1479 
0.0839 
0.1179 
0.1239 
0.0923 


gm. 
0.4947 
0.6308 
0.5213 
0.7605 
0.6654 




0.6958 
0.5295 
0.6710 
0.6611 
0.5408 


Average 




0.5056 


0.1114 


0.6171 






Nutrient solution + 0.5 per cent 


90 
91 
92 
93 
94 
95 
96 
97 
98 
99 


0.3951 
0.3786 
0.5104 
0.3970 
0.4119 
0.3629 
0.4551 
0.7340 
0.6323 
0.5562 


0.0884 
0.0677 
0.0921 
0.0896 
0.0945 
0.0882 
0.0816 
0.1569 
0.1440 
0.0927 


0.4845 
0.4363 
0.6025 
0.4866 
0.5064 
0.4511 
0.5373 
. 0.8909 
0.7763 
0.6489 


Average 




0.4829 


0.0995 


0.5824 







Difference between the solution and agar cultures, —0.0347 gm. or — 5.62 per cent. 

206 



EFFECT OF COLLOIDAL SUBSTANCES ON WHEAT 207 

Silica cultures 

Colloidal silica was prepared by dialysis following in general the method 
used by Graham (4). A preliminary test was made as follows: 

With a pipette approximately 10 cc. of a 10 per cent solution of hydrochloric 
acid were measured into an Erlenmeyer flask. Sodium silicate (a 10 per 
cent solution) was slowly added from a burette while the mixture was shaken 
vigorously. As the sodium silicate increased, the mixture gradually became 
more viscous and finally set to a gel. The amount of silicate solutions 
required to form the gel was then noted. In preparing a quantity of the 
mixture for dialysis, only one-half to two-thirds of the total required sodium 
silicate solution was used. In a mixture of these proportions the silica will 
not set until the chlorides are reduced to a very small percentage. 

Two kinds of dialyzers were used. A very efficient dialyzer was made by 
taking 5 feet of a heavy quality of parchment paper tubing, tying one end 
carefully and then telescoping it into a piece of glass tubing of a little less 
length but of somewhat greater diameter. The end of the glass tube con- 
taining the closed end of the parchment paper tubing was provided with a 
one-hole stopper and a short piece of glass tubing sealed into the hole in this 
stopper. One end of a rubber tube was then attached to the small glass 
tubing, the other end leading to a container of distilled water which furnished 
a head of three or more feet. The parchment paper was always soaked for 
two or three days in distilled water, and carefully tested for leaks. The 
solution to be dialyzed was run into the parchment paper tubing from the 
open end which was then tied and crowded into the glass tube. This end of 
the dialyzer, which was supported about two feet above the opposite end, 
was provided with a one-hole stopper and glass tubing for drainage to the 
sink. A constant stream of distilled water was then forced from the lower 
to the upper end, flowing outside of the parchment tubing and carrying the 
chlorides which diffused through the paper into the drainage. Such an 
arrangement exposes a large surface to a steady stream of water and there 
fore makes a very efficient dialyzer. As we were unable to obtain a sufficient 
amount of the parchment paper tubing for all the work with silica, a modified 
Stern dialyzer was also used. This consists of two pans each of about five 
liters capacity arranged so that a stream of distilled water comes in at the 
bottom of one, fills the pan and overflows evenly at the top. The other pan 
has parchment paper drawn tightly over the top and tied, and a hole made 
in the bottom large enough to insert a funnel. This pan is placed upon the 
first pan bottom up so that the parchment paper comes in contact with the 
water in the first pan. Dialysis begins at once when the mixture of sodium 
silicate and hydrochloric acid is put in the top pan. A few short pieces of 
filter paper laid between the two pans help to establish a uniform distribution 
of the water as it flows from the pan. About five liters could be dialyzed at 
one time with this apparatus which requires a period of nearly three weeks 



208 



DAVID STOUT JENNINGS 



with the water running continuously. As dialysis continues, the viscosity of 
the sol gradually increases, finally setting to a gel. The extent to which the 
silica can be purified before setting depends, of course, upon the concentration 
of the silica. Thus in one case with 2.8 per cent of silica, gelation began when 
nearly 5000 p.p.m. of chlorides were present, while in another case with 1.5 
per cent of silica, gelation did not begin until the chloride content was re- 
duced to 700 p.p.m. The silica was never allowed to set firmly in the dialyzer, 
but was siphoned into a large container and then enough measured into the 
culture jars to give 1 per cent of silica when diluted to 500 cc. The dilu- 
tions were made from the standard nutrient solution or from this solution 
and distilled water. Before measuring the colloidal silica solution into the 
jars for the cultures, total solids and chlorides were determined and the 
latter calculated as sodium chloride. As it was not practicable to remove all 
chlorides from the silica, sodium chloride was added to the cultures con- 
taining no silica so that all culture media contained the same amount of 

TABLE 4 

Dry weights of wheat seedlings grown for 27 days in pure nutrient, solutions and in nutrient 
solutions containing 1 per cent silica 



TREATMENT 



Nutrient solution 85 p.p.m 

Nutrient solution 85 p.p.m. + silica 1 per cent. . 

Nutrient solution 250 p.p.m 

Nutrient solution 250 p.p.m. + silica 1 per cent. 



DRY WEIGHT OF 
TOPS 


INCREASE DUE TO SILICA 


gm. 


gm. 


per cent 


0.3627 






0.4276 


0.0649 


17.8 


0.4594 






0.5936 


0.1342 


29.2 



sodium chloride. Wheat plants were selected, threaded into corks and 
transferred from tap water to the culture solutions in the manner described 
for agar cultures. Within two to three days the plants growing in nutrient 
solutions containing 1 per cent of silica were larger and had better color than 
those growing in pure nutrient solutions. This difference was maintained 
until harvest. The results of this experiment are given in table 4. 

The weights of roots are not given in the above table since it was not always 
possible to make an accurate separation from the adhering gel. 

The figures in table 4 show that the silica was decidedly beneficial to the 
wheat seedlings. It occurred to the author that the effect might be due to 
increased absorption of silica by the plant. Determinations of silica in the 
seedlings showed that the suspicion was well founded. The data may be 
seen by reference to table 5. An attempt was made to obviate this dis- 
turbing factor by introducing into one set of cultures 50 p.p.m. of colloidal 
silica, on the assumption that this amount would supply the requirements 
of the plant for silicon. Accordingly, three sets of cultures were set up in 
the manner already described. Four concentrations of nutrient salts* were 
used. The data are given in table 5. 



EFFECT OF COLLOIDAL SUBSTANCES ON WHEAT 



209 



TABLE 5 

Dry weights and silica content of wheat seedlings grown in nutrient solutions and in nutrient 

solutions containing silica 



TREATMENT 



Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 
Nutrient 



solution 85 p.p.m 

solution 85 p.p.m. -f- colloidal silica 50 p.p.m . 

solution 85 p.p.m. + silica gel 1 per cent 

250 p.p.m 



solut: 
solut 
solut: 
solut 
solut 
solut 
solut 
solut 



on 250 p.p.m. + colloidal silica 50 p.p.m. 

on 250 p.p.m. + silica gel 1 per cent 

on 500 p.p.m 

on 500 p.p.m. + colloidal silica 50 p.p.m . 

on 500 p.p.m. + silica gel 1 per cent 

on 1000 p.p.m 

on 1000 p.p.m. + colloidal silica 50 p.p.m , 
on 1000 p.p.m. -f- silica gel 1 per cent 



DRY WEIGHT OF 


SILICA IN DRY 


TOPS 


MATTER 


gm. 


per cent 


0.2628 


5.3 


0.2875 


8.3 


0.4669 


16.0 


0.5635 


3.1 


0.5846 


5.1 


1.0540 


20.2 


0.5743 


2.8 


0.6389 


3.9 


1.1404 


22.8 


0.9688 


2.0 


0.7961 


3.6 


1.4235 


31.3 



The results show a striking correlation between silica in the culture medium, 
growth of plant, and silica in plant. The medium does not, therefore, fulfill the 
requirement of an inert colloidal substance and is, therefore, not suitable for 
the problem undertaken in this study. The data are given merely for the 
benefit of those who may wish to undertake similar work. 

Sand cultures 

The amount of salt adsorbed from a solution by an adsorbent depends 
upon the surface exposed by the adsorpent. If a change in the concentration 
of the nutrient salts due to adsorption is sufficient to modify the production 
of dry matter in plants, the difference ought to be increased when the fineness 
of the adsorbent is increased. Quartz sand was selected as the adsorbent on 
the assumption that being very insoluble it would not supply nutrients to the 
plant. Three different grades of sand were secured from the New England 
Quartz Company of New York City. These are known commercially as 
no. 000, 1 and 2. A mechanical analysis is given in table 6. 

The sands were purified by heating with hydrochloric acid (1:3) for about 
ten hours, washing with distilled water until free from chlorides, thoroughly 
drying and storing for future use. 

In growing plants either in soil or in water cultures it is necessary to re- 
place the water lost by transpiration and evaporation. With water cultures 
this renewal is accomplished either by adding at frequent intervals sufficient 
distilled water to maintain the original volume or by discarding the old 
medium entirely and adding fresh nutrient solution equivalent to the original 
amount of the old. The second procedure is preferable since it eliminates 
the possible accumulation of toxic excreta. With quartz sand cultures 
renewal of solutions has not been practiced. The method used by McCall 



210 



DAVID STOUT JENNINGS 



in which solutions were renewed but old sand retained did not take into 
account the possible saturated condition of the quartz after continual use. 
The writer has devised a method for renewing not only the nutrient solutions 
but also the quartz. 

For this purpose glass fruit jars of 1 pint capacity were used. A hole \ 
inch in diameter was drilled in the bottom of each jar. The holes were 
stoppered and plants which had been selected and threaded into the corks 
were transferred to the jars which were to be used in the experiment. A 
volume of 250 or 300 cc. of nutrient solution of the desired concentration was 
transferred to the jar by means of a funnel, a large hole having previously 
been made in the cork for this purpose. Seven hundred grams of quartz 
sand was then weighed, a large funnel inserted in the hole of the stopper, and 
the sand allowed to fall gently into the solution. By using a small scoop and 



TABLE 6 
Mechanical analysis of quartz sands 



Fine gravel (2-1 mm.) 

Coarse sand (1.0-0.5 mm.) 

Medium sand (0.5-0.25 mm.) 

Fine sand (0.25-0.1 mm.) 

Very fine sand (0.1-0.05 mm.) . . . 
Silt and clay (less than 0.05 mm.) 



NUMBER 2 



per cent 

0.08 
21.09 
68.93 
8.45 
0.16 
0.86 



99.57 



NUMBER 1 



per cent 




2.25 

92.51 

1.91 

3.29 



99.96 



NUMBER 000 



per cent 

1.53 
2.63 
8.93 
69.62 
12.27 
4.78 



99.76 



sprinkling the sand into the funnel the stream of sand falling into the solution 
could easily be regulated. The roots of the plants were completely buried 
in the sand. At renewal periods the old sand and solution were removed by 
first taking out the small stopper at the bottom of the container, and then 
allowing a gentle stream of distilled water to run in at the top, the cork 
holding the plants remaining in place. Being under a low head this water 
never ran swiftly. A large glass siphon was used, and to give flexibility to 
that end which was inserted through the hole in the stopper containing the 
plants, a piece of rubber tubing was attached. The fresh solution and sand 
were added in the same manner as the first addition. 

All solutions were renewed twice per week. The checks were solution 
cultures and were grown in the same amount and same concentration of 
nutrient solution as the sand cultures. The distilled water used in all cultures 
was treated with carbon black. The process of renewal just described ap- 
pears not to be detrimental to the seedlings, as the comparison in table 7 will 
show. 



EFFECT OF COLLOIDAL SUBSTANCES ON WHEAT 



211 



TABLE 7 

Dry weights of wheat seedlings grown in quartz to which nutrient solutions were added 





WEIGHTS OF SEEDLINGS GROWN IN 




Quartz sand 
number 2 


Quartz sand 
number 000 


Nutrient solution and sand renewed twice each week 

Nutrient solution and sand not renewed, but distilled 
water added 


gm. 

0.6551 
0.5089 


gm. 

0.8033 
5888 







* These figures indicate a better development where solutions were renewed. 

In tables 8 and 9 are given the results of experiments showing the effect of 
quartz sands of different degrees of fineness on the growth of wheat. 

TABLE 8 

Dry weights of wheat plants grown 35 days in nutrient solutions with and without quartz 
sand of different degrees of fineness. 

(Concentration of nutrient solution 750 p. p.m.; sand and nutrient solution changed twice 
per week.) 



TREATMENT 


DRY WEIGHT OF WHEAT SEEDLINGS. TOPS ONLY 






1 


2 


3 


4 


5 


6 




Nutrient solution 

Nutrient solution + 

sand no. 2 

Nutrient solution + 

sand no. 1 

Nutrient solution + 

sand no. 000 


gm. 

0.2624 
0.2158 

0.2382 
0.1911 


gm. 

0.2717 
0.2440 
0.2245 
0.2298 


gm. 

0.2011 
0.2362 
0.2279 
0.2179 


gm. 

0.2816 
0.2448 
0.2280 
0.2356 


gm. 

0.2449 
0.1920 
0.2368 
0.1984 


gm. 

0.2339 
0.2663 
0.2312 
0.1842 


gm. 

0.2492 
0.2332 
0.2311 
0.2073 



TABLE 9 



Dry weights of wheat plants grown for 28 days in nutrient solutions with and without qnartz 
sand of different degrees of fineness. 

(Concentration of nutrient solution 370 p. p.m.; sand and nutrient solution renewed twice 
each week.) 



TREATMENT 


DRY WEIGHT OF WHEAT SEEDLINGS. TOPS ONLY 


AVERAGE 




1 


2 


3 


4 


5 




Nutrient solution 


gm. 

1.0442 
0.6827 
0.8749 


gm. 

1.1595 
0.6175 
0.8826 


gm. 

1.0149 
0.6871 
0.8930 


gm. 

1.2198 
0.6696 
0.6370 


gm. 

1 . 1670 
0.6038 
0.8743 


gm. 

1 1211 


Nutrient solution + sand no. 2 . . 
Nutrient solution + sand no. 000. 


0.6551 
0.8033 



212 DAVID STOUT JENNINGS 

It will be seen that the amount of dry matter produced is greater for a 
nutrient solution of a given concentration than for the same concentration 
in sand cultures. Although the differences are small, it seems sufficient to 
indicate that the decrease in concentration of the nutrient solution by the 
sand may be a factor causing a smaller production of dry matter. 

Ferric hydroxide cultures 

It occurred to the author that hydroxides of iron and aluminum might be 
suitable for a study of adsorption. These substances are relatively insol- 
uble, are colloidal in character, and supposedly would not furnish nutrients 
to increase plant growth. The ferric hydroxide was prepared as follows: A 
10 per cent solution of chemically pure ferric chloride was prepared and 
placed in a large bottle. Ammonium hydroxide was then added carefully 
until the mixture was faintly alkaline to litmus. The bottle was then filled 
with distilled water, stoppered, shaken thoroughly, and allowed to stand until 
the precipitate had settled. The supernatant liquid, was siphoned off and the 
washings repeated until free from chlorides. After the last washing the sus- 
pension was allowed to settle for several weeks and the supernatant liquid 
drawn off. A sample of the remaining suspension was used for determination 
of the ferric hydroxide and the remainder used in the cultures to be described. 
The cultures were made up so that all solutions contained the same con- 
centration when calculated on a basis of total volume of water and total 
nutrient salts. Sufficient ferric hydroxide suspension was used to give 1.5 
per cent ferric hydroxide calculated on volume of culture solution. The 
plants were grown in glass tumblers of 300 cc. capacity, the plants being 
previously selected and threaded into corks and placed in the different cul- 
tures. In all cases the entire medium was renewed twice each week. The 
results of the experiment are given in table 10. 

No difference could be seen in the general appearance of the ferric hy- 
droxide cultures and the checks during the early part of the growing period, 
except that the latter in most cases developed a heavier growth. Towards 
the end of the growing period, however, the plants in the ferric hydroxide 
cultures had a somewhat darker green color. The duration of the growing 
period was in every case determined by the plants in the iron, there being a 
more marked yellowing of the ends of the leaves in these cultures. These 
effects may result from an excessive use of iron in the metabolism of the 
plant, although, in view of the work of Gile and Carrero and from the insol- 
ubility of the colloidal iron, this would not seem to be the case. 

In every case the dry weight of the tops is less for the plants grown in ferric 
hydroxide cultures. 

The colloidal ferric hydroxide adheres to the roots forming a very tenacious 
covering. The roots were always washed carefully in distilled water before 
drying, but it was impossible to remove all of the iron oxide from them. 



TABLE 10 



Dry weights of wheat plants grown in nutrient solution and in nutrient solution containing 
ferric hydroxide calculated as YeiOz 



TREATMENT 



WEIGHT OF TOPS 
ONLY 



Length of growing period- 


— 5 weeks 






gm. 


gm. 




0.4042 






0.5175 






0.4355 






0.6204 






0.5456 
0.5479 
0.4456 
0.5531 
0.5372 






. 0.4485 


0.5056 




0.3706 






0.3283 






0.4044 




Nutrient solution 750 p.p.m. + ferric hydroxide 1.5 
per cent 


0.5868 
0.4408 
0.3499 










0.3507 






0.3457 






0.4374 






0.3876 


0.4002 



Length of growing period — 30 days 



Nutrient solution 750 p.p.m . 



Nutrient solution 750 p.p.m. + ferric hydroxide 1.5 
per cent 



1.2430 
1.7361 
1.9641 
1.6378 
1.6540 

0.8435 
1 . 1832 
0.7775 
0.7405 
0.9629 



1.6490 



0.9015 



Length of growing period — 31 days 



Nutrient solution 370 p.p.m . 



Nutrient solution 370 p.p.m. + ferric hydroxide 1.5 
per cent j 



1.1147 
1.3210 
1.6747 
1.5611 
1.5614 
1.4955 

0.9688 
0.9892 
1.1689 
1.0984 
1.0029 
1.0927 



1.4894 



1.0535 



213 



SOIL SCIENCE, VOL. VII, NO. 3 



214 



DAVID STOUT JENNINGS 



Aluminum hydroxide cultures 

The procedure already described for the preparation of ferric hydroxide was 
followed in preparing the aluminum hydroxide, the chloride of aluminum 
being used in the place of ferric chloride. The suspension was made of such 
strength that the cultures contained 2 per cent of aluminum hydroxide cal- 
culated as AI2O3. The experiment was performed at the same time and 
under the same conditions as were the ferric hydroxide cultures. The results 
are given in table 11. 

TABLE 11 

Dry weights of wheat plants grown in nutrient solution and in a nutrient solution containing 
2 per cent of aluminum hydroxide calculated as AI2O3 



TREATMENT 



WEIGHT OF TOPS 
ONLY 



Length of growing period — 31 days 



Nutrient solution 370 p.p.m . 



Nutrient solution 370 p.p.m. + aluminum hydroxide 
2 per cent < 



Nutrient solution 750 p.p.m . 



Nutrient solution 750 p.p.m. treatment with AI2O3 . . 



Nutrient solution 750 p.p.m. + aluminum hydroxide 
2 per cent i 



gm. 
1.1147 
1.3210 
1.6747 
1.5611 
1.5614 
1.4955 

1.1188 
1.4504 
1.2624 
1.1612 

1.6490 

1.3607 
1.4984 
1.3131 
1.5164 

1.4411 
1.6344 
1.1921 
1.7367 
1.5414 



1.4894 

1.2481 
1.6490 

1.4222 



1.5091 



Difference between nutrient solution (treated) and nutrient solution with AI2O3 gm. 
- 0.0530, per cent - 2.8. 



The results in table 11 show that aluminum hydroxide is similar to ferric 
hydroxide in that its addition to nutrient solutions caused a decrease in the 
growth of the wheat plants. 



EFFECT OF COLLOIDAL SUBSTANCES ON WHEAT . 215 



SUMMARY 



The effect of adding agar to nutrient solutions was to increase the growth 
of wheat seedlings in low concentrations and to decrease the growth in higher 
concentrations of nutrient salts. The introduction of colloidal silica into 
nutrient solutions resulted in increased weight of wheat seedlings. The 
increase was apparently due to direct absorption of silica by the plant and not 
to a change in the effective concentration of the nutrient solution. Silica gel 
is, therefore, considered unsuited for studies of the character described in this 
paper. The introduction of quartzs and, ferric hydroxide, and aluminum hy- 
droxide into nutrient solutions resulted in decreased growth of wheat seed- 
lings. It appears that these substances by their absorptive properties reduce 
the effective concentration of the nutrient solution. 

REFERENCES 

(1) Breazeale, J. F. 1916 Effect of certain solids upon the growth of seedlings in 

water cultures. In Bot. Gaz., v. 41, p. 54-63. 

(2) Dandeno, J. B. 1904 The relation of mass action and physical affinity to toxicity. 

In Amer. Jour. Sci., s. 4, v. 17, no. 102, p. 437-458. 

(3) Gile, P. L., and Carrero, J. O. 1916 Assimilation of iron by rice from certain 

nutrient solutions. In Jour. Agr. Res., v. 7, no. 12, p. 503-528. 

(4) Graham, T. 1861 Liquid diffusion applied to analysis. In Phil. Trans. Roy. Soc, 

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(5) Gregoire, A. 1911 L'action sur les vegetaux superieurs de quelques sels hydro- 

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(6) Jensen, G. H. 1907 Toxic limits and stimulation effects of some soils and poisons 

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(7) Livingston, B. E. 1907 Further studies on the properties of unproductive soils. 

U. S. Dept. Agr. Bur. Soils Bui. 36. 

(8) Lyon, T. L., and Bizzell, J. A. 1917 The plant as an indication of the relative 

density of soil solutions. In Proc. Amer. Soc. Agron., v. 4, p. 35-49. 

(9) McCall, A. G. 1916 Physiological balance of nutrient solutions for plants in sand 

cultures. In Soil Sci., v. 2, p. 207-253. 

(10) Nageli, C. von 1893 tjber oligoddynamische Erscheinungen in lebenden Zellen. 

In Denkschr. Schweiz. Naturf. Gesell., Bd. 33, p. 1-21. 

(11) Schreiner, O., and Failyer, G- H. 1906 Colorimetric, turbidity, and titration 

methods used in soil investigations. U. S. Dept. Agr. Bur. Soils Bui. 31. 

(12) True, R. H., and Oglevee, C. E. 1904 The effect of the presence of certain in- 

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(13) True, R. H., and Oglevee, C. E. 1905 The effect of the presence of certain in- 

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